Electrical ignition and control system for fuel burner



March 3, 1970 J. B. MELLETT ET AL 3,498,731

ELECTRICAL mnmou AND CONTROL SYSTEM FOR FUEL BURNER Filed July 1. 1968INVENTOR @waay ATTORNEY United States Patent 3,498,731 ELECTRICALIGNITION AND CONTROL SYSTEM FOR FUEL BURNER Jesse B. Mellett,Zionsville, and Tilford W. Sutterfield, Indlanapolis, Ind., assignors toStewart-Warner Corporation, Chicago, Ill., a corporation of VirginiaFiled July 1, 1968, Ser. No. 741,430

Int. Cl. F23n 5/00 US. Cl. 431-63 6 Claims ABSTRACT OF THE DISCLOSURE Atemperature responsive switching circuit for a fuel burner which employsan assembly of resistances having positive temperature coefficientsresistance for insuring a constant low voltage aross the blower motorand the resistance igniter during burner start-up regardless of voltagefluctuation.

Vehicular liquid fuel burners normally include a battery or other sourceof voltage for supplying the required electrical energy for both theelectrical ignition means and a blower motor which forces combustion airto pass through the burner. Igniters in the form of electricalresistance coils have been employed for initially igniting the fuel andair mixture whereupon the resultant flame sustains combustion and theignition means are deenergized. On the other hand, the blower motorremains continually energized to deliver the required combusion andventilating air.

One type of electrical resistance ignition means is set forth inco-pending United States Patent application, Ser. No. 741,73 8, whichemploys an ordinary automobile cigarette lighter which consists of athin disc-like resistanc coil of many turns which conventionallyoperates on direct current of 12 volts such as that delivered by anautomobile battery. Since extended operation of this resistance igniterat 12 volts would burn it out, it is necessary to operate the same atless than 12 volts and preferably not much over 10 volts despite batteryvoltage variation. In turn, the blower motor which supplies bothcombustion and ventilating air must be operated during burner startup atsomething less than full battery voltage and thereafter for a very shorttime since, if the blower motors were placed across full battery voltageit would rotate at high speed, and the high velocity air would quenchthe flame.

In order to insure the required reduction in voltage across both theseelements during start-up, there has been suggested various schemes foraccomplishing this purpose, such as complicated and expensivetransistorized voltage control circuits and the like. Ordinary voltagedropping elements which are conventional resistances or potentiometersare useless since the voltage across the motor and the resistanceigniter would correspond to the applied battery voltage which is likelyto change irrespective of need.

It is, therefore, a primary object of this invention to provide animproved voltage control system for a burner resistance igniter and anelectrical blower motor wherein the voltage across both of theseelements is maintained at a desirable low value during burner start-up,regardless of battery voltage fluctuation.

It is a further object of this invention to provide an improved ignitionand blower motor control system for a liquid fuel burner which isextremely reliant, inexpensive, and places the blower motordirectly-across the battery subsequent to the production of the stableflame.

It is a further object of this invention to provide an improved ignitionand blower motor control system which insures operation of the blowermotor at low speed during 3,498,731 Patented Mar. 3, 1970 ICC ignitionstart-up, regardless of supply voltage fluctuation but readily allowshigh speed blower operation subsequent to establishment of a sustainedflame.

Other objects of this invention will appear from examination of thefollowing detailed description and the claims together with theaccompanying drawing which disclose, by way of example, the best modecontemplated to date by the applicant for applying the principles of theinvention.

In the drawings:

FIGURE 1 is a perspective view of the improved multiple resistorassembly forming a portion of the control circuit of the presentinvention.

FIGURE 2 is an electrical schematic view of the ignition and controlcircuit of the present invention.

In general, the improved ignition and control system for the fuel burnercomprises a normally closed flame detector switch for selectivelycoupling respective resistance elements of positive temperaturecoefficient of resistance in series with the blower motor and theelectrical resistance igniter during blower motor start-up and burnerignition. The flame detector switch further operates in response to asustained flame to place the blower motor directly across the voltagesource and disconnect the resistance igniter.

A compact resistor assembly forming a part of the circuit comprisesthree, spaced fixedly positioned, generally parallel flat glass filledepoxy wafers, each carrying a resistance element having a large positivetemperature coefficient of resistance in the form of a helical coil withthe coil turns in contact with the wafers at opposed edges only wherebythe resistance elements are truly responsive to the current generatedheat for maintaining the desired low voltage across the igniter andblower motor during ingition and start-up.

Turning to FIGURE 2 of the drawings, the ignition and control circuit ofthe present invention advantageously employed three resistance elements10, 12 and 14 as the voltage regulating means for both the resistancetype igniter 16 and the blower motor 18. It is important to note thatthe resistance elements 10, 12 and 14 have positive temperaturecoeificience of resistance such that as their temperatures increase dueto current passage therethrough their resistance values rapidly increaseby 3 to 4 times. The resistance wire used may comprise an alloy of 70%nickel and 30% iron manufactured under the trade name Balco by theWilbur B. Driver Co. of Newark, NJ. This characteristic is in contrastto the normal characteristic of electrical resistance elements in that,as the current increases their resistance increases slightly.

Circuit control is achieved manually through ignition switch 20, andheater switch 22 to efl'ect initial energization of both the electricalresistance heater 16 and the blower motor 18. Deenergization is achievedautomatically through the flame sensitive switch carrying normallyclosed contacts 26 and 28, respectively. A battery 30 or other source ofelectrical current has one side grounded, and the other connected to theheater switch 22 through the normally open ignition switch 20. Heaterswitch 22 employs a movable, normally opened switch contact 32 whichcloses to deliver current through fixed contact 34 to the burner supplycontrol means (not shown) through line 36. The other movable contactmember 38 selectively delivers electrical current from battery 30 to thecontrol elements including flame detector switch 24 associated with boththe resistance igniter 16 and the blower motor 18. Fixed contact 39 iscoupled through line 40* to resistance elements 10 and 12, these twoelements being directly connected in series through tie bar 42. Line 40terminates at fixed contact 44 of the flame detector switch 24. Flamedetector switch 24 is conventional, and is carried by and within thecombustion chamber of the fuel burner, in such a position that asustained flame impinges directly upon the end 46 of the flame detectorswitch. This causes rod-like member or armature 48, due to thermalexpansion of the tube carrying the same, to move vertically downwardfrom the position shown, to open the normally closed movable switchcontact 26. The movable switch contact 26 is coupled directly to theblower motor 18 through line 50, the opposite side of the blower motorbeing ground. The flame detector switch is of the double throw, doublepole type and includes a second movable switch member 28 deliveringelectrical current from line 50 through lead 52 to stationary contact54. The electrical resistance igniter 16 is series coupled with thethird resistance element 14 by means of line 56 and stationary contact54. Line 60 connects fixed contact 58 to line 40 bypassing resistors and12. In response to a sustained flame the movable switch member 26 movesaway from fixed contact 44 and moves into contact with fixed contact 58to complete a circuit between battery 30 and blower motor 18, bypassingseries connected resistors 10 and 12. Simultaneously, armature 62, whichmechanically couples the flame detector movable switch contacts 26 and28, causes the resistance igniter 16 and its series resistance 14 to bedisconnected from voltage source 30.

In the resistor assembly of FIGURE 1, the fact that the resistorelements 10, 12 and 14 have large positive temperature coeflicients ofresistance, enables the control system to operate satisfactorily. Theresistance elements 10, 12 and 14 are each wound in a helix onrespective fiat glass filled epoxy wafers 64, 66 and 68, respectively,the wafers being supported in spaced fashion upon a pair of transverserods 70 and 72 which are coupled at their ends to respective L-shapedsupport plates 74 and 76. Note in FIGURE 1 the employment of the lowresistance tie bar 42 to directly connect resistances 10' and 12, whileat the opposite end, leads 40 and 41 allow connection to the heaterswitch 22 and fixed terminal switch contact 44 of the flame detectorswitch 46. Lead 56 couples resistance element 14 to fixed contact 54 ofthe flame detector switch while lead 57 connects the resistance igniter16 thereto. The winding of each of the resistance elements 10, 12 and 14on insulated support wafers is such that the resistance wires are incontact with the wafers only at the notched edges. The wires are thusspaced from the wafers and do not tend to lose their heat through thewafers. The loops are spaced closely enough so that they contribute toheat conduction between themselves. Thus, the resistance values of therespective resistance elements 10, 12 and 14 are truly dependent uponthe heat generated by the electrical current passing therethrough. Themiddle resistance element, since it is used only for igniter control,does not require as many turns and is not spaced as far from the wafersas the other two. The unused notches on each side for additional wireturns are plainly visible in FIG. 1. The resistance elements aresuitably coupled to their respec tive leads by conventional wafercarried terminal members 82.

The operation of the ignition control circuit will be described inconjunction with typical values being applied to the elements formingthe system. For instance, the voltage source 30 may comprise aconventional 24 volt automobile battery and the circuit may employ twolarge series connected resistance elements 10 and 12, having a totalresistance of approximately .37 ohms at 68 F. With switches 20, 22 and24 closed, these resistances will carry about 11 amps with the currentgenerating sufficient heat to bring the temperature of the resistancesto about 1000 F. The positive temperature coeflicients of resistancelying in the range of 300' to 400% change are in great contrast to thoseof conventional resistances in which the normal increase is less than10% for this temperature range and may, in fact, be negative. At 1000F., the resistance value of the two resistances 10 and 12 approaches twoohms. This greatly reduces the current passing both to blower motor 18and the resistance igniter 16. Further, the third resistance element 14has its resistance changes from a value of approximately .13 ohms at 68F. to .6 ohms at 1000" F. with this resistance carrying approximately 6amps of current. The result is that the voltage drop across the firsttwo resistance elements 10 and 14 increases within seconds after thecircuit is initially closed to reduce the voltage across the motor 18 toa desired value of between 11 and 13 volts, depending on batteryvoltage. Of course, immediately upon closing of the switches 20 and 22,a large voltage is available to the motor 18 for starting, but withinseconds, this voltage is greatly reduced to insure slow blower speed toprevent quenching of the flame. During ignition and start-up, the thirdresistance element 14 is series connected with resistance elements 10and 12 and the resistance igniter 16 and, thus, brings the voltageacross the resistance igniter 16 down to a value which lies between 9 /2and 10 /2 volts, regardless of battery fluctuation.

Meanwhile, upon the creation of a sustained flame within the burner, theimpingement of the same on the end 46 of the flame detector switchcauses the expanding tube surrounding solid rod 48 to force movableswitch contacts 26 and 28 away from the fixed contacts 44 and 54,respectively. The opening of contacts 28 and 54 deenergizes theresistance igniter 16. Contact 26 in moving from fixed contact 44 tofixed contact 58, causes the blower motor 18 which is operating at lowspeed due to the series resistors 10 and 12, to be placed directlyacross the available supply voltage from battery 30, whereupon, theblower motor 18 continues to operate at high speed due to increase ofcurrent flow, Operation continues until burner shutdown, in which case,the flame detector switch 10 again moves to the position shown in FIGURE2, that is, a normally closed position. Upon reenergization of thecontrol and ignition circuit, by closure of ignition switch 20 andheater switch 22, ignition is achieved with controlled blower motoroperation in repeat fashion.

Because of the large change in resistance of elements 10, 12 and 14 withincrease in temperature, fluctuations in I battery voltages are largelyimmaterial. For example, a

nominal 24 volt battery may deliver 28 volts but, with the presentcontrol circuit the igniter voltage is less than 10 /2 volts and themotor voltage is likewise retained within desired limits. At lowerbattery voltage the resistors will not become as hot and, therefore,their resistances will be considerably smaller leading .to aproportionately smaller voltage drop and thus maintain voltages in thedesired range between 9 /2 and 10 /2 volts for the resistance igniterand between 11 and 13 volts for the blower motor, The same circuit, ofcourse, may be important for systems incorporating a 12 volt supplyrather than the 24 volt supply shown. At the same time, while the largeresistance elements 10 and 12 are shown as being positioned on eitherside of the small resistance element 14 in a three part assembly, it isobvious that resistance elements 10 and 12 may be united and carried bya single flat glass-filled epoxy wafer. The resistance wire employed inthe winding of resistance elements 10, 12 and 14 may comprise anymaterial having the desired positive temperature coeflicient ofresistance and may be, for example, formed of iron and nickel wire, suchas those manufactured under the aforementioned trade name Balco.

While the invention has been particularly shown and described withreference to a preferred embodiment, it will be understood by thoseskilled in the art that the foregoing and other changes in form anddetails may be made therein without departing from the spirit and scopeof the invention.

What is claimed is:

1. In a fuel burner including an electrical resistance igniter, avoltage source and a normally closed temperature responsive flamedetector switch for coupling said voltage source across said resistanceigniter, the improvement comprising: first resistance means in serieswith said resistance igniter, said first resistance means having apositive temperature coefiicient of resistance, a blower motor fordelivering combustion air to said fuel burner, second resistance meanshaving a positive temperature coe'lficient of resistance, and meanscarried by said temperature responsive flame detector switch forconnecting said second resistance means in series with said blower motorand across said voltage source during ignition.

2. A control system for a fuel burner, including an electricalresistance igniter, a blower motor, a source of voltage, said systemcomprising first and second resistance means having positive temperaturecoefficients of resistance, and a flame detector switch for selectivelycoupling said first and second resistance means and said resistanceigniter in series and across said voltage source, and said firstresistance means and said blower motor in series and across said voltagesource in the absence of a flame, and for disconnecting said resistanceigniter from said voltage source, and connecting said blower motordirectly across said voltage source in response to a sustained burnerflame.

3. In a control system for a fuel burner as set forth in claim 2,wherein said resistance means includes an assembly having a plurality oflongitudinally spaced resistance wire supporting wafers, means forfixedly positioning said wafers on a support member in spaced parallelfashion, resistance elements carried by respective wafers in the form ofhelical coils of resistance wire having positive temperature coeflicientof resistance, with the turns of said coils being in contact with thewafers along only the edges.

4. The assembly as claimed in claim 3, further including notches carriedby the opposed edges of said wafer for spacing said resistance wireturns to insure contact of said turns and said water support at theedges thereof,

5. The assembly as claimed in claim 3, having three Wafers formed offlat glass-filled epoxy, with the number of resistance wire turnscarried by said central wafer being less than the number of turns of theouter two wafers, said resistance wire comprising an iron-nickel alloy.

6. The assembly as claimed in claim 3, further including a lowresistance tie bar coupling the ends of the two outer resistance wirecoils.

References Cited UNITED STATES PATENTS 2,685,917 8/1954 Perry 43 l63 XCARROLL B. DORITY, JR., Primary Examiner US. Cl. X.R. 33822

